Capacitance electronic discs have been developed which when played back on the appropriate player will produce signal information similar to a conventional television broadcast signal. If the signal information produced on playback of a capacitance electronic disc is supplied to a conventional home television receiver, the programming recorded on the disc can be reproduced on the television receiver.
In the capacitance electronic disc system the video and audio signal information is pressed into a plastic disc in the form of surface relief variations in the information track of the disc. During playback of the plastic disc a capacitive electronic pickup system converts the surface relief variations into electrical signals as described by J. K. Clemens in "CAPACITIVE PICKUP AND THE BURIED SUBCARRIER ENCODING SYSTEM FOR THE RCA VIDEO DISC", RCA Review 39, P. 33, March 1973, which is incorporated by reference into this specification.
The carrier-to-noise ratio of the video and audio signals obtained on playback of the capacitance electronic disc to a large extent define the limits of the quality of playback of the disc. In general, the higher the carrier-to-noise ratio, the higher will be the quality of the reproduction of the recorded programming. While precise lower limits for carrier-to-noise ratios cannot be given as there is a gradual corresponding decrease in signal quality with a decrease in the carrier-to-noise ratios, it appears that for commercially acceptable playback on a conventional television receiver, the video signal carrier-to-noise ratio should be above about 50 dB and the audio carrier-to-noise ratio should be above about 25 dB.
The losses in the carrier-to-noise ratio of the recording as compared to the original programming occurs at various stages in the manufacture of capacitance electronic discs, such as, in the recording of the signal information in the recording substrate, the replication of the recording substrates to make masters, the manufacture of the molds and stampers, and the molding of the plastic capacitance electronic discs.
One area where considerable problems have been encountered with regard to losses in the carrier-to-noise ratios is in the replication of the recorded substrate to produce masters. The recording of the programming information for a capacitance electronic disc is made in a metal recording substrate. The recording for the capacitance electronic discs must be made in metal substrates, as opposed to lacquer substrates used for conventional stereo audio records, because of the extremely small size of the video and audio signal elements and the extreme accuracy of recording required for capacitance electronic discs. The information track containing the signal information is cut in a layer of a relatively soft metal, such as electrodeposited bright acid copper. The surface of the recorded metal substrate is then passivated and masters are electroformed and removed from the recorded surface of the recording substrates.
A problem which has been encountered with the metallic recording substrates, and in particular with copper recording substrates, is that there can be a substantial decrease in the carrier-to-noise ratio for both the video and audio signals as a result of masters being formed on and removed from the recording substrate. This reduction in the carrier-to-noise ratio is the most critical factor which determines the useful life of a recording substrate. A further, and even more serious, problem is that some metallic substrates, and in particular copper substrates prepared as noted above, often exhibit a very substantial drop in the carrier-to-noise ratios after only a few masters are formed on the substrate. This unexplained phenomenon is difficult to explain in that it is not encountered with all substrates and some of the substrates that are affected will recover most of the lost carrier-to-noise ratio after a few unsatisfactory masters are made on the substrate.
Another serious problem that is encountered with the prior art recording substrates is that microdefects often develop in the recorded area of masters formed on the substrates. The term microdefect as used herein refers to defects such as bumps or pits which appear in the recorded area of the masters, molds and stampers. The microdefects are relatively small, from about 5 to 20 micrometers or slightly larger. However, because of the narrow width of the information tracks and the small size of the signal elements, the microdefects can extend over a number of information tracks and can cause a problem which is referred to as "lock groove" in which the same information track will be repeatedly played on playback, or "skip groove" wherein a number of information tracks will simply be passed over during playback of the video disc.
What would be highly advantageous would be an improvement in the method for the manufacture of metallic recording substrates for capacitance electronic discs which would reduce losses in the carrier-to-noise ratios which occur during replication and which would reduce the number of microdefects in resulting masters.